One form of catalytic converter presently being manufactured has an oval-shaped catalyst coated substrate made from an extruded ceramic located within an oval-shaped housing with dual wall end cones. The end cones cooperate to form air chambers at the opposed ends of the converter that serve to reduce the outside temperature of the converter and also serve to block the hot exhaust gases from impinging directly on a mat material located between the substrate and the housing.
One problem with a converter of this type is that, when the substrate together with the mat material is stuffed into the oval housing, the outer oval configuration of the housing can distort. As a result, the outer end cones which fit onto the opposed open ends of the housing are required to have large tolerances to accommodate the varying outer configurations of the housing. This then, causes some difficulty in welding the end cones to the housing. Another problem is that during high temperature operation of the converter, there is a tendency for the housing to expand along the minor axis so as to reduce the density of the mat which, in turn, reduces the life of the mat material.
It has been proposed (see SAE Technical Paper 922340, entitled "Effect of Header Truncation on Monolith Converter Emission-Control Performance", authored by Daniel W. Wendland et. al. and presented in October 1992 at the International Fuels and Lubricants Meeting and Exposition) to shorten the distance between the inlet and outlet tube and the substrate to approximately one inch. The single wall end cone design prevalent at that time, however, presents a further problem in that the mat material supporting the substrate is exposed to hot exhaust gases which, if the catalytic converter is placed in a location close to the vehicle engine where the exhaust gas temperature at the inlet of the catalytic converter is sufficiently high, will tend to erode the mat resulting in a loss of substrate retention and heat insulating capability of the mat material.